The three novels follow three characters during the two-year period between the original Final Fantasy VII game's ending and the beginning of the Advent Children movie: Tifa, Barret, and...Denzel. Don't remember Denzel? He's the young boy who appears in Advent Children as a victim of Geostigma. Adult!Denzel tells his story because he wants to enlist in the World Regeneration Organization, which is being run by former Shinra head Reeve (also known as Cait Sith).
This isn't Final Fantasy VII's first anime-- an OVA titled Last Order, which told the story of Zack's unfortunate demise and came out with the Advent Children Ultimate Edition. And It's no Final Fantasy VII game remake. But it's probably going to be pretty cool.